chore/#40: PositionDropdownPreview 네이밍 변경

Author: jinukeu

feature/signup/src/main/java/com/yapp/feature/signup/signup/component/PositionDropdown.kt

@@ -137,7 +137,7 @@ fun PositionDropdown(
 
 @Preview(showBackground = true)
 @Composable
-fun PreviewYappBasicInputTextWithDropdown() {
+private fun PositionDropdownPreview() {
     YappTheme {
         var selectedValue by remember { mutableStateOf<String?>(null) }